btrfs: fix leak of kobject name for sub-group space_info

When create_space_info_sub_group() allocates elements of
space_info->sub_group[], kobject_init_and_add() is called for each
element via btrfs_sysfs_add_space_info_type(). However, when
check_removing_space_info() frees these elements, it does not call
btrfs_sysfs_remove_space_info() on them. As a result, kobject_put() is
not called and the associated kobj->name objects are leaked.

This memory leak is reproduced by running the blktests test case
zbd/009 on kernels built with CONFIG_DEBUG_KMEMLEAK. The kmemleak
feature reports the following error:

unreferenced object 0xffff888112877d40 (size 16):
  comm "mount", pid 1244, jiffies 4294996972
  hex dump (first 16 bytes):
    64 61 74 61 2d 72 65 6c 6f 63 00 c4 c6 a7 cb 7f  data-reloc......
  backtrace (crc 53ffde4d):
    __kmalloc_node_track_caller_noprof+0x619/0x870
    kstrdup+0x42/0xc0
    kobject_set_name_vargs+0x44/0x110
    kobject_init_and_add+0xcf/0x150
    btrfs_sysfs_add_space_info_type+0xfc/0x210 [btrfs]
    create_space_info_sub_group.constprop.0+0xfb/0x1b0 [btrfs]
    create_space_info+0x211/0x320 [btrfs]
    btrfs_init_space_info+0x15a/0x1b0 [btrfs]
    open_ctree+0x33c7/0x4a50 [btrfs]
    btrfs_get_tree.cold+0x9f/0x1ee [btrfs]
    vfs_get_tree+0x87/0x2f0
    vfs_cmd_create+0xbd/0x280
    __do_sys_fsconfig+0x3df/0x990
    do_syscall_64+0x136/0x1540
    entry_SYSCALL_64_after_hwframe+0x76/0x7e

To avoid the leak, call btrfs_sysfs_remove_space_info() instead of
kfree() for the elements.

Fixes: f92ee31e ("btrfs: introduce btrfs_space_info sub-group")
Link: https://lore.kernel.org/linux-block/b9488881-f18d-4f47-91a5-3c9bf63955a5@wdc.com/


Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>